The background of the invention will be discussed in two parts.
1. Field of the Invention
This invention relates to hydraulic presses, and more particularly, to a hydraulic press cylinder arrangement for equalizing forces in the event of unequal loading of the press.
2. Description of the Prior Art
In punch presses, the workpiece is positioned on a table, and either the table or a platen carrying the die is moved relative to the other. The general construction of such hydraulic presses consists of one cylinder located centrally relative to the fixed posts or frame that make up the structure of the press. In such structures, reliance is placed on the frame to maintain a parallel attitude between the platen and table. In many instances, unequal loading exists when working pressures vary.
In some hydraulic presses, this movement is accomplished by hydraulic cylinders, usually an even number such as two or four, positioned at opposite sides or at opposite corners of a platen, thus surrounding the load with pressure on all sides. Although this would appear to have some merit, in truth, without unequal loading and multiple cylinders, the lesser loaded cylinder will receive more fluid, thus creating a cocking or tilting between the platen or table, or between the upper and lower platens. Various attempts have been made to provide some means for maintaining the parallel relation between the table and platen by elaborate hydraulic mechanisms and valving. Some such systems employed rack and pinion couplings, cable and pulley couplings, and crank and lever couplings to maintain the proper attitude. Other attempts have included complicated valve control systems to overcome the problem.
Exemplary of the prior art is U.S. Pat. No. 2,976,798 entitled "Level Operating Multiple Ram Press," issued to Christianson on Mar. 28, 1961, the patent disclosing an arrangement for hydraulic presses in which a series of primary cylinders are utilized equal in number to the secondary or ram cylinders of the press, with a confined hydraulic circuit for each cylinder. The pistons of the primary cylinders are tied together mechanically in axially-aligned relation, and the pistons of the ram cylinders are also tied together mechanically.
U.S. Pat. No. 3,023,676 is issued to Howahr et al. on Mar. 13, 1962, and is entitled "Hydraulic Presses," such patent disclosing an hydraulic forging press which includes a cross-head and two chain-link-shaped members forming two parallel pairs of columns of rectangular section which are slidable longitudinally relative to the cross-head, with the cross-head carrying one platen or die and the other platen or die being carried on a cross-beam extending between adjacent ends of the link-shaped members.
Another press apparatus is shown in U.S. Pat. No. 3,324,704, entitled "Press Brakes," issued to Savory on June 13, 1967, such patent showing a brake apparatus for bending metal in which a piston rod on one side is coupled to a connecting member which may be pivoted out of the way for access to the workpiece.
A press with leveling means is shown and described in U.S. Pat. No. 4,157,066, entitled "Presses Having Platen Leveling Means," such patent issuing to Pretty on June 6, 1979, the hydraulic mechanism having provision for restricting fluid flow return from a cylinder when one column of the press advances relative to another, preferably on diagonally-opposite columns.
Another hydraulic system is shown and described in U.S. Pat. No. 4,161,229, issued to Mifsud on July 17, 1979, such patent being entitled "Hydraulic Synchronizing System for Coordinating Movements of the Vibrator Guide Rods," the system including a double-piston power source and a drain valve in fluid communication with the hydraulic lift cylinders of a vehicle-mounted vibratory seismic energy source. The double-piston power source supplies the lift cylinders with substantially equal volume of hydraulic fluid, and the drain valve adjusts the flow of hydraulic fluid out of the lift cylinders.
Accordingly, it is an object of the present invention to provide a new and improved hydraulic press and method of actuation thereof.
It is another object of the present invention to provide a new and improved hydraulic cylinder arrangement for use in a hydraulic press.
It is a further object of the present invention to provide a new and improved hydraulic system with an air or oil booster actuating a ram member through a plurality of axially aligned chambers with a ram section in each chamber having a cross-section of different area with each chamber in fluid communication with a cylinder of the press.